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Britain's opposition Labor leader Ed Miliband will say on Monday that Prime Minister David Cameron's pledge to hold a referendum on European Union membership will subject business to two years of chaos if the Conservatives win the election.

Campaigning in Britain's closest national election in decades will start on Monday after Queen Elizabeth dissolves parliament at Cameron's behest, teeing up an unusually fraught battle to govern the $2.8 trillion economy.

Cameron, whose Conservatives are neck and neck with Labor in most polls, has promised to renegotiate Britain's EU ties ahead of a referendum by the end of 2017 if he wins on May 7.

In a full-page advert in the Financial Times newspaper on Monday featuring quotes from business leaders, Labor warns the threat of a British exit from the EU is "The biggest risk to British business".

"There could be nothing worse for our country or for our great exporting businesses than playing political games with our membership in Europe," Miliband will say at a speech in London later on Monday, according to extracts released in advance.

"It is a recipe for two years of uncertainty in which inward investment will drain away, two years of chaos in which businesses will not be able to plan for the future, and two years of wasted opportunities for progress, for profit, for prosperity: a clear and present danger to British jobs, British business and British prosperity."

Cameron, whose party is better trusted to run the economy according to opinion polls, will on Monday warn that a Labor government risked "economic chaos" and would put up taxes.

Some in the business community have accused Miliband of demonizing big business and fear his plans for a more hands-on approach to regulation in sectors like banking and energy could make Britain less attractive to investors.

Speaking to the Telegraph newspaper, businessman and Labor donor Assem Allam said several of Labor's policies, including a plan for an extra tax on high value properties and a higher top rate of income tax, "penalizes" wealth creation and said the Conservatives were stronger on the economy.

"This is in the genes of the Conservative Party, their ability to get the economy of the country on the right track. In actual fact I believe they are the best party in Europe in managing the economy," he said.